My Favorite Auto-Focus Setting

Are you satisfied with the AF capabilities of you camera? I find the AF of the Canon 30D adequate, but not great. Sometimes it hunts a bit and sometimes it focuses all the way to infinity and back before it finds the focus plane. And when shooting with a tele, the plane of focus is not always exactly where I wanted it to be. But I guess all users of all cameras have similar problems from time to time and since these are only occasional, I don’t think that the AF of my camera is faulty. Assuming that your AF works properly, what kinds of settings do you use for the kind of shooting that you do? I’ve gone through several “evolutions”:

“AI Focus AF” and all AF sensors active. The “AI” stands for “artificial intelligence” and makes a Canon camera use some fuzzy logic to determine when to do single-shot AF and when to do continuous AF. But this setting had several problems. First of all, fuzzy logic is unpredictable, and the camera was not always doing what I was hoping it would do. Furthermore activating all AF sensors makes the camera focus on the closest thing that any of the AF sensors are pointing at. For portraits the focus is always on the tip of the nose and not on the eyes, and it’s a nuisance focusing through grass or a fence or things like that.

Pretty soon I switched to single point AF and of course chose the center point. This worked better. I’d aim the camera so that the thing that I want to be in focus is covered by the central AF sensor, press the shutter half-way, then recompose and take the photo.

Since I don’t shoot any sports, I also switched to one-shot AF. In 98% of all situations this was the right setting, and for the other 2% I manually switched to continuous AF.

I also experimented with selecting AF points other than the central one, but this had some disadvantages: for many shots the points are not ideally located, the interface for choosing the active point is OK, but still not as fast as I’d like it to be. Also, after taking a shot I’d leave the active AF point unchanged, so I had to do it before the next shot, which caused me to lose some shots.

So I went back to using only the central point and “focus, recompose, shoot.” That coupled with single-shot AF worked very well for me for a long time.

But if I wanted to take several shots of something which off center and not moving, the “focus, recompose, shoot” thing was getting irritating. And what if the camera gets the focus wrong? I’d have to adjust it manually before each shot!

What I actually needed was a way to activate the AF at will and not each time I released the shutter. And luckily, Canon offers such a way, using custom function 4, “Shutter/AE Lock button.” By choosing setting 1, “AE lock/AF,” you turn the exposure-lock button (the one with the * on it) into an AF button and the half-press of the shutter-release activates the exposure lock. It takes a few days to get used to this, but after a while it feels perfect! You aim your camera at something, press the * button and the thing comes in focus. Now you move the camera around, looking for a good composition. When you do, you press the shutter-release completely. For further shots you don’t activate the AF at all, you just press the shutter-release. This has three positive effects: no more “focus, recompose, shoot,” you use less battery juice, and you have a way of fine-tuning the AF plane between shots. This last point is important, because with the standard setting the AF gets activated before each shot and you have no constant reference across the shots.

OK, so at this point I was a pretty happy camper… until I got to India. In Germany I hadn’t done much street shooting (who does?), but in India there is so much action in the street that you are constantly switching from one person to the next. Some are static, but many are moving — the single-shot AF was not working very well any more.

Now I use the following AF settings: custom function 4 set to 1, continuous AF and only the central AF point is active. This way I can press the * button shortly for static subjects, then think about composition, exposure, etc. Or I can press it continuously for moving subjects. I can even hold it pressed and release the shutter at the same time. It works extremely well for me! WARNING: if you decide to try the custom function 4 idea, don’t do it before a major shoot! You’d forget that your AF is not automatically active, and you’d screw half of your pictures. Try it when you have a week or two of leisure shooting and gradually get used to the new functionality. QUESTION: Do camera makers other than Canon offer a similar functionality — moving the AF away from the shutter-release button?

Do camera makers other than Canon offer a similar functionality — moving the AF away from the shutter-release button?

K20D has separate AE-Lock and AF buttons. There are many settings to customize behaviour of these buttons, like
* whether shutter should activate autofocus or not
* whether shutter should also act like AE-lock
* for AF button I can choose it to either
– activate focusing
– deactivate focusing (i.e. while holding it, shutter will not autofocus)
– set central AF point (in mode which allows manual choosing of AF points)

So, the question to your question is yes, with K20D I can disengage autofocusing from shutter and activate it by AF button.